6 Answers
6

Cell phones have tiny lenses, tiny image sensors, which add noise, lose detail and have indifferent contrast. High-frequency data (hair, fur, grass) is the first and most obvious victim, so that should also be your first target for the simulation.

The best place to start, since you have Photoshop, is in Adobe Camera Raw. Open the jpeg into ACR from Bridge (right click and choose "Open in Camera Raw").

Set the Clarity slider to -100. You can also reduce the Contrast slider, if necessary.

Increase Recovery AND Fill Light to reduce contrast.

Adjust Tint, Temperature and Exposure until sufficiently yucky.

Somewhat counter-intuitive: go to the Sharpen module and over-sharpen the image, highest radius and maybe 70% sharpen. All noise reduction sliders to 0.

In Split Toning, add blue to the shadows and yellow to the highlights (or vice versa, just so they're different).

Here's an image before:

And after:

Note that this is quite different from the effect you'd get using any of the Blur filters in Photoshop, but is a good match for the loss of detail in a typical camera phone.

Now open the image in Photoshop.

To get some noise into the image, Alt/Option Click the New Layer icon and set the new layer to Overlay mode. Select "Uniform" for the Check the "Fill with 50% gray" box and UNcheck "Monochromatic" (you want color noise). Play with the settings until you have something close to the effect you want (it will be too sharp-looking, but we'll fix that in the next step):

To get the blotchy look of small-sensor color noise, finesse the noise layer with the Shape Blur filter. You can experiment with different settings. On my test image, 10 pixels worked well using the starburst shape:

This technique makes very realistic sensor noise in the darker and bluer areas of the image, which is where they are normally most noticeable in the "real thing."

Your second example is not a bad camera, but rather bad lighting, causing the shutter speed to slow down, causing a motion blur. The focus also seems a bit off as well, or perhaps it is just a large aperture setting, which would again come down to the lighting.

It seems to me that you are not being very specific on what effect that you want. The second photo is a lighting / camera setting issue, but the camera is decent. The first and third picture are indeed bad cameras, but before I looked at the examples, I immediately thought of one of those really crappy .gif's from years back that were all over the web, like this:

This is an example of both a bad camera (that is blowing out all of the highlights; this was done with a second layer with 50%, linear dodge blending options -- color dodge might be more to your liking, though) and bad compression (64-color .gif.)

This could be made even more accurate with "levels" adjustments, adjusting the exposure (low-quality cameras often cannot adjust properly to lighting,) etc., but you'd really need a perfect example of what you want in order to anyone to really nail it... otherwise we can only guess.